The blood-brain barrier (BBB) explains why certain substances circulating in the blood are able to get into the brain and others do not. The BBB is formed by brain capillaries that look like simple tubes of endothelial cells. Experimental and clinical evidence suggests that the BBB maintains the chemical environment for neuronal function and protects the brain from harmful substances. Every year millions of dollars are spent by pharmaceutical companies to develop and test drugs using in vitro models of the BBB, many of which end up not working in vivo. Studies performed in small animals including rodents cannot be directly extrapolated to human tissue. Preliminary results from this and other laboratories have convincingly demonstrated that use of rodent brain endothelial cells and in general endothelial cell lines from non human sources as models of clinical pharmacology are sometimes imperfect. In fact, while a number of drug resistance molecules are expressed in rodent brain, the human brain appears to be much more complicated as demonstrated by both clinical and in vitro observations. Conversely, most of the promising CNS drugs that are effective in vitro have failed clinical trials due to disease- related appearance of the multidrug resistance phenomenon. We propose to develop and validate a humanized, practical in vitro model of the BBB that more accurately reflects the clinical reality of the BBB. In particular, we wish to 1) compare the BBB permeability of clinically relevant antiepileptic drugs in pharmacorespondent patients to values measured in an in vitro model comprised of cells from the same subjects or other sources of normal, non-epileptic, non drug resistant human brain. This will be achieved by measuring serum and brain antiepileptic drug levels intraoperatively or in vitro;and 2) to compare BBB permeability values of the same drugs measured in multiple drug resistant patients to values measured in an in vitro model comprised of cells from the same subjects. This will be performed by measuring the penetration of drugs into multiple drug resistant human brain and across cells isolated from human brain during surgeries to relieve refractory seizures. PAR-07-049 wishes to "accelerate the process of drug discovery" and to "Develop cellular assays that permit the preliminary screening of compounds". We strongly believe that improving the predictive value of in vitro models of the blood- brain barrier is a crucial step in this direction. The experiments proposed herein will however have a profound impact on the success of high-throughput screening of putative CNS drugs. PUBLIC HEALTH RELEVANCE: One third of patients with epilepsy have drug-resistant epilepsy, which is associated with an increased risk of death and debilitating psychosocial consequences. The basis of drug resistance in human epilepsy is not understood. Parallels with resistance in cancer suggest that drug resistance proteins may have a role. We believe that blood vessels of multiple drug resistant epileptics are lined with molecules that extrude drugs from the brain, causing an impediment to successful relief of seizures. If our hypothesis is correct we may acquire new tools to treat epilepsy in children and adults.